Bulkable composite polyester yarn of continuous filaments having different residual shrinkage after boiloff



May 20, 1969 c. E. REESE 3,444,681

BULKABLE COMPOSITE POLYESTER YARN OF CONTINUOUS FILAMENTS HAVING DIFFERENT RESIDUAL SHRINKAGE AFTER BOILOFF Filed March 8, 1966 mvsmon CECIL E. REESE ATTORNEY United States Patent U.S. Cl. 57-140 2 Claims ABSTRACT OF THE DISCLOSURE Composite, continuous-filament polyester yarn is disclosed which is composed of differentially shrinkable filaments capable of developing bulkiness subsequent to conversion to fabric, and after the fabric is secured and dyed, when heated at temperatures above 100 C. during dry textile finishing operations. The yarn is preferably prepared by melt spinning filament species of the same chemical composition but substantially different relative viscosities, annealing the higher relative viscosity species during spinning to have approximately the same natural draw ratio as the other species, combining and drawing the two species to at least the natural draw ratio, and heat-setting the drawn yarn.

This invention relates to continuous-filament polyester yarns having components of different shrinkage characteristics which cause the composite yarn to become bulky when shrunk. It is more particularly concerned with bulkable composite polyester yarn in which bulkiness develops primarily at temperatures above 100 C., as in the fabric heat-setting step of conventional fabric finishing. The invention is also directed to a process for producin such yarn.

In the conventional process for melt-spinning polyester filaments, molten polyester is extruded into filaments through a spinneret, the filaments are solidified by quenching in an air stream and are simultaneously attenuated to a lower denier by pulling them away from the spinneret, the filaments are then drawn to at least their natural draw ratio, and the drawn filaments are heat-set or heat-relaxed to reduce the residual shrinkage. The drawing operation imparts molecular orientation and increased crystallinity to provide improved properties in the filaments, e.g., higher tenacity and lower elongation. It is important that the filaments be drawn to at least the natural draw ratio, since less complete drawing results in drawing of intermittent lengths to the natural extent but essentially no drawing of the intervening segments. The resulting yarns have a harsh tactility and will dye unevenly. The filaments can be hot drawn to more than the natural draw ratio, but too much drawing results in undesirable filament breaks and poor mechanical properties.

The above operations can be carried out under different conditions to provide yarns which differ in boiloff residual shrinkages. Such shrinkage usually occurs after weaving or knitting when the fabric is given a detergentscour to remove sizes or yarn finishes, or during a dyeing operation. Maerov et a1. U.S. Patent No. 3,199,281 dated Aug. 10, 1965, discloses producing yarns having dilferent residual shrinkages in this way and then combining the yarns to form a composite yarn which becomes bulky when subjected to hot-wet treatment.

Full realization of the bulking capacity of the fabric without undesirable non-uniformity in appearance, resulting from filament buckling in a non-random manner, is dependent on a number of factors, e.g., a construction which is selected to be suitably leaner than desired in the bulked fabric, proper level of yarn twist, random dis- 3,444,681 Patented May 20, 1969 tribution within the yarn of the filament species having different boilolf residual shrinkages, and absence of tnesion on the fabric during the shrinking process. This latter requirement has been troublesome to realize in a scouring operation. Most synthetic fiber yarns and fabrics may also be treated at a higher temperature while dry to bring about the bulk-inducing shrinkage in those cases where the fabric is not so tightly constructed as to inhibit bulk development. Such treatment is frequently used in fabric heat-setting to ensure dimensional stability, but the heat-setting step occurs so late in the usual sequence of fabric-finishing steps that ordinary yarns have already been shrunk by the prior hot-wet treatments involved.

This invention provides a process for producing a novel composite yarn which bulks as a result of differences in shrinkability among species of individual filaments in response to dry heat-treatment. It further provides such bulkable yarn comprising two or more species of filaments which retain a useful degree of differential shrinkability after treatment in water at the boil. It also provides fabrics of improved tactility and cover and of superior uniformity. Other advantages will be recognized as the description proceeds.

In the drawings, which illustrate a preferred embodiment of the process and certain apparatus used therein,

FIGURE 1 is a schematic representation of a spinning and drawing process, and

FIGURE 2 is a perspective view of a device for annealing filaments as they are spun.

The bulkable continuous-filament polyester yarn of this invention is a composite of two or more filament species which differ in molecular weight of polyester and in shrinkage at 180 C. The filament species are composed of polyester of essentially the same chemical composition but the molecular weights, as determined by relative viscosity (RV) measurements, differ by at least about 8 units. Preferably there is a difference of about 10 to 40 in relative viscosity between two species. The higher RV filament species has a percent shrinkage at 180 C. which is at least about 3 units greater than the percent shrinkage at 180 C. of the lower RV filaments. The composite yarn has a boiloff shinkage of 1% to 7%, is essentially free of harsh, incompletely drawn filament segments, and is capable of developing the major part of its potential bulkiness during dry textile finishing at temperatures above C.

In a preferred process for producing the above yarn, a linear ethylene terephthalate polyester is melt spun to form filaments having a relative viscosity of 15 to 30, and a polyester of essentially the same chemical composition but of a higher relative viscosity than the first polyester is melt spun to form filaments having a relative viscosity at least about 8 units higher than the first filaments. The higher RV filaments are annealed during spinning, by exposing them to heat of the order of 350420 C., to have approximately the same natural draw ratio as the lower RV filaments. The filament species are then drawn to at least the natural draw ratio and heat-set at 165 to have a boiloff shrinkage in the range of 1 to 7% The filaments may be combined to form the composite yarn at any time after formation of the filaments and annealing of the higher RV filaments. The filaments may be combined before or after drawing, and before or after heat-setting. The process can be interrupted at any of these steps, by collecting the filaments either as separate yarns or after combining them, and subsequently continuing the process. The filaments can be processed separately through all of these steps and then be combined subsequently. The filaments can be combined by any of the methods known to the art, such as interlacing, plying with true twisting, false twisting, etc. It will usually be desir- 3 able to carry out the entire process as a continuous operation, and the filaments are preferably combined before drawing. In this preferred process the annealing of the higher RV filaments must be controlled so that smooth drawing of the combined filaments to at least the natural draw ratio without filament breakage can be achieved.

It is desirable that the annealing be controlled so that break elongations of the two filament species differ by no more than 10% after drawing, and preferably by no more than In some cases widely different break elongations may be obtained even though the filaments of higher relative viscosity polymer are annealed to result in smooth drawing of both filament species as described above. In these cases a further fine adjustment in annealing temperature may be made, an increase tending to increase the break elongation of the filaments of higher relative viscosity and vice versa.

All species of filaments in the composite yarn should have nearly the same natural draw ratio. This may be attained, for example, by adjustment of annealing conditions just below the spinneret to provide exposure to higher temperature (more annealing) for the species comprising the higher relative viscosity (higher molecular weight) polymer. Such species are thereby increased in natural draw ratio. They serve as the higher-shrinkability filament species of the composite yarn.

The polyester compositions of the filaments represented by the several species of filaments may differ in relative viscosity from 8 up to a value limited only by the range of spinnable molecular weights under a given set of spinning conditions. The greater the range of molecular weight difference among species the greater is the dry-heat-shrinkability-differential and, hence, the bulk of the finished fabric.

The normal boilolf shrinkage of drawn polyester yarn is in the range of 55-12% or more. The filaments of the composite yarn of this invention are heat-set at 135 to 165 C. after drawing, on hot rolls or by other means known in the art, so that the composite yarn has a boilofi shrinkage in the range of 17%. Preferably there is less than 2 units difference between the boilofi shrinkages of the filament species in the yarn.

The bulkable yarns of this invention are handled in a completely standard manner through the usual textile processing operations. Development of the desired bulk is dependent only on providing the proper amount of shrinkage, or retraction, during the heat-setting operation, which may employ, for example, the commonly-available tenter frames.

Relative viscosity (RV) refers to the ratio of viscosity of a solution of the polymer in a mixture of 10 parts of phenol and 7 parts of 2,4,6-trichlorophenol (by weight) to the viscosity of the solvent itself, both measured at 25 C. and expressed in the same units.

A schematic drawing of the preferred process of this invention is shown in FIGURE 1, although it is to be understood that many variations may be used in the process without departing from the spirit and scope of this invention. As illustrated, a linear polyester is fed through conduit 1 to spinneret pack 2, and is extruded from spinneret 3 to form filaments 4. The filaments are pulled downward and converged to form yarn 7 by passage partly around feed roll 5 and its separator roll 6. Concurrently, a linear polyester of higher relative viscosity is fed through conduit 8 to spinning pack 9, and is extruded through spinneret 10 and annealing device 11 to form filaments 12. The annealer 11 surrounds the filaments as they leave the spinneret face and is heated to a temperature higher than that of the filaments. The filaments 12 are converged into yarn and pass partly around feed roll 13 and its separator roll 14, which travel at the same peripheral speed as feed roll 5 and separator roll 6. Yam 7 and yarn 15 converge at draw pin 16, which is partially immersed in draw fluid 17 contained in draw pan 18. The combined yarn travels partially around draw pin 16, partially around .4 auxiliary pins 19 and 20, and is drawn by draw rolls 21 and 22 to form drawn yarn 23.

The annealing device 11, referred to above, is suitably of the form shown in FIGURE 2.

The annealer comprises a metal cylinder 25 surrounded by insulating material 26. Heating element 27 passes in spiral configuration intimately around cylinder 25. A thermocouple 28 measures the temperature of the cylinder. A mounting bracket 29 is used to mount the annealer close to the spinneret.

When using polyethylene terephthalate, the temperature of the annealer should be heated to a temperature at which the filaments will be subjected to a temperature of from approximately 350 to 420 C. adjacent to the spinneret face. If the annealer temperature is much lower than the said minimum, high-heat shrinkage differential of the yarn components is negated; conversely, if the annealer temperature is much higher than the said maximum, undesirable thick and thin portions are obtained in the spinning filaments of the annealed yarn. At even higher annealer temperatures the polymer drips from the spinneret.

Bulkmay be developed in the yarn prior to its being woven to a fabric, but the stated advantages are most pronounced when the yarns are bulked subsequent to their conversion to fabrics, and preferably after the fabrics are scoured and dyed.

The invention is further illustrated by the following examples, which are not intended to be limit-ative.

Example I Two 99 denier, 25 filament yarns of poly- [ethylene terephthalate/S-(sodium sulfo)isophthalate] (98/2) are separately melt-spun. The copolyesters used are of difierent relative viscosity (RV). Yarn (A), prepared from the higher RV copolyester, has a relative viscosity of 30.7 and the filaments are subjected to an annealing temperature of 396 C. for about 0.1 second immediately after emergence from the spinneret. The other yarn (B) is spun from copolyester of identical chemical composition but of lower relative viscosity to give 16.5 RV yarn, and the filaments are not annealed during spinning. The two yarns are merged on-the-run between spinning and drawing to provide a composite yarn which is drawn 3.0x, i.e., the yarn is drawn to a length which is 3.0 times the length prior to drawing. The yarn is heat-set on the draw roll at 157 C. Small lots of each individual yarn processed through drawing in a hot water bath separately and heat set on heated rolls to provide samples for testing the properties of individual yarn species. Results are tabulated in Table 1.

TABLE 1 Both Yarn A Yarn B together Spun fiber RV 30. 7 Annealer temp. C 396 Draw ratio 3. 0 Draw bath temp C. 94-9 Draw speed, output (y.p.m.) 2, 000 2, 000 2, 000 Yarn properties:

Denier 33 33 66 M1 .p.d.) 83 95 92 Tenacity (g8). 3. 2 3. 0 3. 3 Elongation percen 11.3 27 10. 9 Shrinkage (percentage):

Boilofi 5. 9 4. 1 5. 8 180 0. dry 13. 7 9. 7 14. 6

Example 11 Filaments of trilobal cross section (as described in Holland US. Patent No. 2,939,201 dated June 7, 1960), are prepared by the procedure of Example I from two poly(ethylene terephthalate) polymers of 16.3 and 53.7 RV, respectively. In this case, the filaments of the polymer of higher RV are annealed by exposure to 375 C. for eight inches immediately after the filaments emerge from the spinneret. Conditions and results are summarized in Table 2.

indicated in Table 4. The co-spun yarns are combined to form a composite yarn prior to drawing.

TABLE 2 5 TABLE 4 Y A Y B Both am am toge her High RV Low RV together Polymer RV 53. 7 16. 3 s

pun fiber RV 33 25. 3 Annea1er.temp' (a 375 none Annealer temperature O) 350-360 None Draw ratio 4. 3 4. 5 4. 3 Draw ratio 5 5 5 Draw speed, output (y.p. 2. 2,550 Draw speed y.p.m. (hi 7111p. 2, 000 2,000 2, 000 YEY%PI?PBMBS= 22s 829 1, 829

9 33 33 68 Yarn Properties: M1 (g.p.d.).. 115 125 123 Denier 30 32 68 Tenacity (g.p.d.) 5.6 4.3 5.0 Mi m 134 119 94 Elongatwn (pe cent) 7 5 2 Tenacity f,j 6 8 5 shnnkiage (percent): Elongation (percent) 17 26 27 Bollofi- 9 1 6 1O Shrinkage (percent);

0 C 17.3 10.0 15.7 BUM 4. 5 3 1 5 14.7 11 7 12.4

Example 111 Two filament yarns of the copolyester composition The yarns of Examples I-IV are woven into plainemployed for Example I and having 31.6 and 15.4 RV, Weave fabrics after twisting the warp yarns by a combinarespectively, are separately melt-spun and packaged in the tion of 3 turns downtwist and 4.5 turns uptwist to 7.5 turns as-spun condition. The higher-RV itemds subjected to Z. Filling yarns are downtwisted to 3Z. The warp yarns are 420 C. for eight inches immediately after the filaments 25 twist-set by heating at 58 C., 75% RH for 1 /2 hours and emerge from the spinneret. The lower-RV item is not anwithout added moisture for an additional /2 hour. Fillnealed. ing yarns are not heat-set. The fabrics are finished as The two separate yarns are combined for drawing by indicated in Table 5. feeding them over a common guide surface and are drawn The values for Bulk are determined as follows: 2.4x with heat-setting on the draw roll. Properties of the A single thickness of the fabric is laid on a base surface individual species of filaments are determined on small of precise flatness and a glass disc, having a weight of TABLE '5 Bulk Heat 3 Heat 3 set Loom Finished Yarn Identification Scour treat (C.) (0. Fabric Wt. count count B3 B40 B 239 Example 1 183 1. 25 94 x 72 104 x 80 s. 1 2. 2 2. 1 Example 2-- 185 2. 29 90 x 72 108 x 90 2.8 2.6 2. 3 Example 3 182 1. 96 94 x 72 107 x 83 3.0 2. 6 2. 3 Example 3 4 180 2. 14 94 x 72 116 x 86 2. 7 2. 4 2. 2 Example 4 4 170 1. 91 90 x 72 107 x 85 2. 7 2. s 2. 3 70 dten./ fil. trilobal basic-dyeable poly- .do t 180 2.10 114 x 78 124 x 82 1.8 1. 7 1. 7

es er yarn. 70 den/5O fil. trilobal poly(ethylene do 5 180 2. 10 114 X 78 125 x 81 1.9 1.7 1. 7

terephthalate) yarn.

Heated for 30 minutes in an open vessel at 90-94" C., using a surfactant to assure complete wetting and sodium pyrophosphate as a buffer.

2 Scour-ed tensionless for 2 passes at 0., 2 passes at 70 C., 2 passes at 80 C. and 4 passes at 95 C.

amounts of the individual yarns which are drawn separately. Properties are summarized in Table 3.

Yarns of 33 and 25.3 RV, respectively, are prepared from poly(ethylene terephthalate) by simultaneous meltspinning and drawing with heat-setting. Conditions are 3 Time is 5 minutes, except as noted, 7% overfeed and 7% underwidth. 5 seconds at no over-feed and about 2% underwidtll.

3 gms./cm. and precisely parallel faces, is laid on the fabric. Exact measurements of the height of the upper face of the disc from the base surface are compared with the height of the upper face of the disc when laid directly on the base surface. The volume of fabric beneath the glass disc is then determined by a simple calculation and compared with the weight of the same fabric area. The procedure is repeated with discs which have weights of 40 and 238 grams/cmF. Bulk is expressed in terms of cubic centimeters per gram for each of the three loadings.

Results are summarized in Table 5. For comparison, the table also includes results obtained with commercially available single species yarns. The trilobal basic-dyeable yarn is composed of poly[ethylene terephthalate/S- (sodium sulfo)isophthalate] (98/2) polyester of about 22 RV. The other comparison yarns is composed of poly (ethylene terephthalate) polyester of about 25 RV.

The exemplified polymeric compositions and the process conditions employed may be varied substantially while remaining within the spirit and scope of the invention, the critical requirements being only that the two filament species comprise polyesters which differ by at least 8 units in relative viscosity, the filaments comprising the polymer 7 of higher relative viscosity have at least 3% higher shrinkability at 180 C. than the other, the composite yarn have a shrinkage in the range of 1% to 7%, and that the species differ by no more than 10% in break elongation.

I claim:

1. A composite, continuous-filament yarn comprising two filament species of polyester of essentially the same chemical composition, one filament species having a relative viscosity at least 8 units higher than the other species and a percent boiloif shrinkage less than 2 units different from that of the other species, the species of higher relative viscosity having a percent shrinkage at 180 C. at least 3 units greater than that of the lower viscosity species, the composite yarn having a boiloff shrinkage of 1% to 7% and being essentially free of incompletely drawn filament segments.

2. A composite yarn as defined in claim 1 wherein the difference in relative viscosity between said filament species is about 10 to 40 units, the relative viscosity being determined for 10% solutions of the polyesters at 25 C. in a mixture of 10 parts phenol and 7 parts 2,4,6-trichlorophenol by weight.

References Cited UNITED STATES PATENTS 3,039,171 6/1962 Hume et al 28-72 3,199,281 8/1965 Maerov et a1. 57-140 JOHN PETRAKES, Primary Examiner.

U.S. Cl. X.R. 

